1. Field of the Invention
The invention relates to a vibration generator for a vibration pile driver, that comprises imbalance masses that can rotate, which are disposed on shafts. A hydraulic drive having a changeable suction volume is disposed in the generator. The invention furthermore relates to a vibration pile driver having such a vibration generator.
2. The Prior Art
In construction, vibration generators are used to introduce objects, such as profiles, into the ground, or to draw them from the ground, or also to compact ground material. The ground is excited by vibration, and thereby achieves a “pseudo-fluid” state. The goods to be driven in can then be pressed into the construction ground by a static top load. The vibration is characterized by a linear movement and is generated by rotating imbalances that run in opposite directions, in pairs, within a vibrator gear mechanism. Vibration generators are characterized by the rotating imbalance and by the maximal speed of rotation.
Vibration generators are vibration exciters having a linear effect, whose centrifugal force is generated by rotating imbalances. These vibration exciters move at a changeable speed. The size of the imbalance is also referred to as “static moment.” The progression of the speed of the linear vibration exciter corresponds to a periodically recurring function, for example a sine function, but it can also assume other shapes.
Vibration generators are operated with hydraulic drives, which put the shafts on which the imbalances are disposed into rotation. Such hydraulic drives have a power curve that is dependent on the operating speed of rotation and on the operating pressure, respectively. At the same drive power, a higher static moment can be achieved by a lower speed of rotation, thereby bringing about a higher ground vibration, at the same time. In inner city regions, ground vibrations should be avoided. These can be reduced by operating at a higher speed of rotation, but at the same time, the static moment is reduced as a result. These measures prove to be problematic, since the required drive power and the torque are dependent on the speed of rotation. If the hydraulic drive, i.e. motor, leaves its optimal range of operational speed of rotation, this results in a pressure drop. Likewise, the required torque at the motor decreases with an increasing mass of pile-driven material. Accordingly, the pressure gradient at the motor decreases, and only partial use of the drive power that is offered is possible any longer.